Scavenging of two-cycle engines



Aug 18, 1936.. i E. s. DENNISON 2,053,459

SCAVENGING OF TWO-CYCLE ENGINE Filed Dec. 14, 1935 2 Sheets-Sheet 1INVENTOR EDWARD $.DENNISON.

BY allabl M ATTORNEY Patented Aug. 18, 1936 UNITED Y STATES PATENTOFFICE.-

. 1 2,051,409 SCAVENGING or TWO-CYCLE enemas of Pennsylvania aApplication December 14, 1933, Serial 110,702,403

2 Claims. (Cl. 123-65) My invention relates to two-cycle engines and ithas for an object to provide for an improved exhaust and scavengingarrangementso that effective scavenging may be had with a. relativelylarge effective working stroke of the engine.

Itis old tohave a two-cycle engine cylinder provided with opposedscavenge air and exhaust ports; however, this simple arrangementis notvery effective unless the piston is modified to provide for deflectionof the air in order to prevent transverse passage of the air directlyacross the cylinder and out the exhaust ports. A second arrangement hasbeen used wherein a partial belt of scavenge air ports is arranged belowa similar partial belt of exhaust ports, the air crossing the cylinderand being. deflected by the opposite imperforate cylinder wallupwardlyuntil deflected by the head soas to pass downwardly to theexhaust ports, the air path being substantially a loop wherein theoutlet is super-. posed with respect to the inlet. An objection to thesecond arrangement is that the provision of an imperforate cylinder wallto deflect the air upwardly necessitates partial port belts with theresult that the ports have to be made higher than would be the case ifthey extended completely around the cylinder, and, therefore, to theextent that they have to be made higher, to that extent is the workingstroke lessened. A third arrangement has been proposed which constitutesan improvement over the first type in that the air ports are directedradially toward a center disposed eccentrically with respect to thecylinder axis and variously inclined to secure upward travel of the airat one. side of the cylinder, the air being deflected downwardly to theother side by the cylinder head and passing downwardly at the latterside to exhaust ,ports disposed in opposed relation with respect to theair ports;

however this type of construction is also objec tionable because of thenecessary port heightfand the consequent lessened efiective enginestroke .as' compared to an arrangement wherein come,

plete belts or ports are provided.

'llt is "also old to have both scavenge and1ex=f haust' ports extendaround the full perimeter of the-cylinder, the scavenge ports radiatingfrom the 'cylinder axis. 'By thismeans, it. is intended. to produce'acentral iountain'of airmoving up-'. wardly, while th e exhaust gasesfareforced down wardly in the annular spacebetween the air Tool-Q uinn andthe cylinder wall however, this 'a' rangementfsufi ers'from instabilityunlessthe m f i u m ac lnor s ident c l wh fi f efaet iel i-sflfl be;wit t re ult that, the-,1.

air column is thrown ofl center in an irregular and indeterminate wayand undesirable mixing of air and exhaust gases results.

In accordance with my inventiom-I provide a complete belt of exhaustports and a complete belt of scavenge air ports arranged immediatelybelow the'exhaust ports, with the result that a minimum height of portsis involved and a large efiective working stroke is preserved; and, toimpartthe desired directional effect to the air, the air ports radiatefrom a center which is eccentric to the cylinder axis so that theresultant velocity effect of the entering air produces an up- .wardlymoving eccentric column of air disposed toward the side of the cylindernearest to the eccentric center, the air passing upwardly and beingdeflected downwardly to push products of combustion out the exhaustports. By directing Y the air to a locus near one wall, the'upwardmoving column is caused to occupy roughly one half of the cylindersection while exhaust gases occupy the other half and any difilcultybecause of inport height and ,imper'forateness of a'cylinderwall and theadvantage, ofminimum cylinder lengthrequiredfqr-the ports without thedisadvantage of instability of the fourth arrangement;

Therefore, a further object ofrmy. invention is: to provide a tworcyclecylinderawith complete belts of exhaust and scavenge air ports, with thescavenge air portsarranged immediately below the. exhaustpOrtsandradiating from a'zc-enter eccentric totheeylinder axis to securesuchifio'w of air as. to efiectively evict products. of combus-- tionfrom'th cylinder. if If it is resultant air column with respect totheinterior f hefiylii d thi m y. b achieved; by. relay-w esired to change;thelocation; of the tiveIin'clination of the air; ports; forexample, ifv the air port or ports; at. minimumrradius' with respect .to vtheccentriccenter are-.inclined upwardly, the,-.a 1 r,.entering ,throughthe. remainder of the; ports, is rendered more'eifective' toposltion theresultant ;eolumn nearer, :to" the; side-1 or "the cylinder 1 at -the;upwardly inclinedyportsi fincengine so as to obtain the most effectiveopera-- tion, this being done by having the eccentric centers of thescavenge ports arranged in the plane of the crank shaft axis.

These and other objects are effected by my invention as will be apparentfrom the following description and claims taken in connection with theaccompanying drawings forming a part of this application, in which:

Fig. l is a vertical sectional view showing my improved scavengingarrangement;

Fig. 2 is a horizontal sectional view taken along the line 1III of Fig.1 and showing the scavenge air ports;

Fig. 3 is a sectional view taken along the line III-III of Fig. 1 andshowing the exhaust ports;

Fig. 4 is a sectional view of a modified arrangement wherein one or moreair ports are inclined inwardly and upwardly;

Fig. 5 shows a plurality of cylinders grouped so that the scavenge porteccentric centers are in a plane of the longitudinal center line of theengine;

Fig. 6 is a view similar to Fig. 2' but showing a modified arrangementof scavenge ports;

Fig. 7 shows a further modified scavenge port arrangement;

Fig. 8 shows a further modified arrangement of exhaust ports; and Fig. 9is a diagrammatic view illustrative of a fiow principle involved.

Before taking up a description of features of the invention in detail,certain principles and objectives will be considered. A full perimeterofboth scavenge and exhaust ports is desirable to avoiddead spaces and toincrease the eflective stroke of the engine, this arrangement minimizingthe portion of the stroke used for the exhaust and scavenging process.Also, the air should be so controlled that it flows up at one side ofthe cylinder and down at the other, as this produces more orderlyscavenging and provides a minimum area of contact of the upwardly anddownwardlymoving columns, and, therefore, minimizes the admixture of airand exhaust gases. The latter point will be clear from diagrammatic Fig.9. If the air is assumed to move upwardly as a central column, then thedownwardly moving column would be a cylinder thereabout, the contactbeing a circle indicated at a. 0n the other hand,

where the upwardly columnmoves up at one side of the diametral plane band down at the other, the area of contact of the columns is very muchless and is a minimum. In the first case. the cylindrical contact awould be 2.22 times the diametral contact b. In my improved scavengingarrangement, the operation is such that low, or substantially diametral,contact occurs.

In Figs. 1- and 2, I show an engine cylinder Ill having a piston lltherein, the cylinder ll having a head construction I! provided with afuel injection device ll of any suitable type.

' The cylinder is provided with a complete belt of exhaust ports I!which are radially disposed with respect to the cylinder axis I.Immediately below the ports It, the cylinder isrprovided with a completebelt of scavenge air ports II which are disposed substantially radiallywith respect to a center It which is eccentric to the cylinder I 6.

An exhaust manifold 20 receives products of combustion leaving the portsi5 and a scavenge air manifold 2i supplies scavenge air through theports I! to evict products of combustion-from the cylinder. Inoperation, and near the end of a power or working stroke, the piston llfirst uncovers the exhaust ports l5, whereupon there follows a'drop inpressure of the combustion gases and outflow at high velocity ofproducts of combustion through all of the'ports IS, the complete belt ofexhaust ports providing. for

' highly effective action of this kind, while, at the same time,requiring minimum cylinder length for accommodation of the ports. Assoon as the scavengeair ports l'l begin to become uncovered, then thescavenging air is eifective to drive products of combustion out throughthe exhaust ports.

As the exhaust ports 15 and the scavenge air ports I! are arranged asannular belts extending completely around the cylinder andas the portsof each belt are arranged as close together as possible consistent withstrength of the cylinder and cooling thereof and as the belts arearranged close together, it will be apparent that a minimum extent ofcylinder height or length is used to provide the ports, with the resultthat the effective working stroke is maintained at a maxi,-

mum. 1

As will be seen from Fig. 3, the annular belt of exhaust ports radiatefrom the cylinder axis, thereby providing for maximum discharge area,minimum cylinder length for their accommodation and efi'ectivedischarge. 0n the other hand, as may be seen from Fig. 2, the scavengeair ports I I radiate from an eccentric center ll so as to secure, dueto the resultant velocity of air' entering through the ports 11, acolumn of air which moves upwardly at or toward the side of the cylinderhaving ports of minimum radius with respect to the eccentric center, thecolumn of air moving upwardLv and being deflected by the head I! formovement downwardly at or toward the other side of the cylinder to evictproducts of combustion through the exhaust ports.

While all of the scavenge air ports may be disposed horizontally, thearrangement thereof radially with respect to an eccentric centerproviding for the aforementioned fiow eflects given to the air, as shownin Fig. 4, the column of air may be caused to move upwardly more closelybunched to the side of the cylinder by inclining inwardly and upwardlyone or more air ports, indicated at lla. Also, the inclined ports areadvantageous in a directive sense.

In Fig. 5, I show a preferable arrangement of cylinders IO and an airmanifold or box 2!, which communicates with the scavenge ports H of eachcylinder, the cylinders being so disposed that the eccentric unters llfall on the longitudinal center line of the engine. Some throttlingoccurs in the regions 28 between adjacent cylinders; and, to avoid anyinjurious eifect because of lack of flow balance, as would be the caseif'the cylinders were placed so that the relation of the port to themanifold was a random one, the cylinders are placed so that theeccentric centers ll fall on the longitudinal center line of the engine.whereby the flow from each side toward the eccentric centersissymmetrical and upward flow -of air in eachcylinder'isbettercontrolledto minimizethesdmixtureofscavenl eairwith'li gasesf.The symmetrical flow of air into the cylinders on this account isfurther assisted by the provision of equal flow areas 24 at each side ofeach cylinder.

Fig. 6 shows an ,arrangement wherein the scavenge ports I'll) have theircenter lines tangent to a circle 26, the effect of this arrangementbeing to givea swirling motion to the air to aid in combustion.

' Fig. 5 may be employed, the eccentric centers being in the enginelongitudinal center line and the cylinders being left sufliciently blankto either side of the center line, as shown in Fig. 7 at 21 and 28, toavoid any by-passing efiect of the wrist pin bore indicated in dottedlines at 29, the two sets of scavenge ports He, "c of each cylinderbeing directed toward a common center l8; and, as the centers it are, asin Fig. 5, in the plane of the longitudinal center line of the engine,-air will flow in symmetrically from each side toward the centers 18 andupward flow will be better controlled, as heretofore pointed out.

While the arrangements of scavenge air ports are effective to secure theoperations pointed out, nevertheless, it may be desirable in some casesto prevent the possibility of short-circuiting of scavenging airdirectly from the scavenge ports to the exhaust-ports at the arcuateregion of the cylinder nearest to the eccentric center l8. Accordingly,in Fig. 8, I show an alternative form of .my invention wherein thecircumferentially-exest to the eccentric center l8 being omitted. The

scavenge ports are radially disposed with the eccentric center I8 asdescribed in connection with Fig. 2.

From the foregoing, it will be apparent that I have provided anarrangement which gives effective and eflicie'nt scavenging with maximumeflective working stroke of the engine. As shown the scavenge air andexhaust ports are each arranged as a complete annular belt of closelyspaced ports, whereby minimum cylinder length is required for theiraccommodation; and the complete belts or ports facilitate themaintenance of adequate strength in the cylinder and provide for a moresymmetrical structure. The complete annular belt of exhaust portsprovides for effective discharge at high velocity all the way around thecylinder as soon as such ports are uncovered by the piston, this annulardischarge of pf'ifiducts of combustion induced by the pressure dfiipbetween the interior of the cylinder and the exhaust manifold continuingeven after the scavenge air ports begin to open. a

The scavenge-air ports are arranged to promote eii'ective scavenging,they being directed radially toward an eccentric center so as to securebunching of the air at the side of the cylinder adjacent to theeccentric center, the air moving upwardly as a column due to theresultant effect of its velocity energy, and the upwardly moving columnis deflected by the cylinder head for movement downwardly in a bunchedmanner at the other side'to evict products of combustion through theexhaust ports. Thus, it will be seen that, by having the scavenge airports directed toward an eccentric center, the kinetic energy of theenter- .ing air is not dissipated in a turbulent manner withouteffectively scavenging the cylinder, but

the preponderating effect of the velocii'jegergy toward the side of thecylinder at the eccentric center provides an upwardly moving current ofair at the latter side. If desired, the directive tendency of the airmay be aided by inclining upwardly or inwardly one or more of thescavenge air ports at the eccentric center side of the cylinder. It willalso be seen that, by having the eccentric centers in the plane of theengine center line, symmetrical fiow of air into the cylinders andconsequent better control of the upwardly moving air columns areprovided for.

While I have shown my invention in several forms, it will be obvious tothose skilled in the art that it is not so limited but is susceptible ofvarious other changes and modifications without departing from thespirit thereof, and I desire, therefore, that only such limitationsshall be placed thereupon as are imposed by the prior art or as arespecifically set forth in the appended claims.

What I claim is:

1. In a two-cycle engine, a cylinder, complete and superposed annularbelts of exhaust and scavange ports extending through the cylinder walland a piston uncovering the exhaust and scavenge ports=-successively atthe. end of each working stroke, the scavenge ports being disposedEDWARD s. DENNISON.

